1. Field of the Invention
The invention relates to a vacuum processing apparatus and vacuum processing method for carrying out processing on a workpiece, such as plasma etching, plasma CVD, thermal CVD, or sputtering, after vacuum evacuation in manufacturing semiconductor devices, liquid crystal display substrates and the like.
2. Description of the Related Art
The performance of vacuum processing apparatus as represented by semiconductor manufacturing apparatus has become much more demanding with the trend toward higher integration of semiconductor devices and larger area of liquid crystal displays. In plasma etching apparatus, for example, some of the reaction products generated by plasma etching inevitably are deposited to the inside of the etching chamber. The deposits may flake off and fall on the workpiece, causing defects that lead to lower yield of the process. Even if the deposits do not flake off, increase of the deposited reaction products gradually varies the plasma and the reaction balance during processing, which will cause etching defects, while no problem would otherwise occur in the initial state with fewer deposits. In this context, on the production line for semiconductor devices, plasma of fluorine and/or oxygen is repetitively generated once in a certain number of wafers to carry out plasma cleaning inside the chamber for the purpose of removing the reaction products by reacting them with the fluorine or oxygen. However, even such plasma cleaning cannot completely remove the deposits. For this reason, after a certain number of wafers are processed, the vacuum chamber of the apparatus is returned to atmospheric pressure with inert gas such as nitrogen. The vacuum chamber is then opened, wiped with water or volatile chemicals, and subjected to replacement of internal parts. That is, the vacuum chamber of the apparatus is opened to the atmosphere and cleaned throughout the inside. This is referred to as wet cleaning or complete cleaning.
Plasma etching apparatus for producing semiconductor devices may spend tens of percent of the total operating time in the wet cleaning. This decreases time available to the apparatus for actual production. The downtime of the apparatus due to wet cleaning includes not only the time during which the apparatus is actually opened to the atmosphere and cleaned, but also the preceding and following time periods. In particular, wet cleaning must be typically followed by vacuum evacuation until both the chamber base pressure (pressure in the apparatus before process gas is introduced) and the apparent gas inflow rate measured when evacuation is stopped and the chamber is vacuum sealed (the sum of flow rate due to leaks from the atmosphere and flow rate of net outgas from the surface of the chamber itself and its internal components, the sum being hereinafter referred to as leak rate) fall below a prescribed value. This is in order to confirm and ensure that the percentage of other gases mixed in the process gas is below a prescribed value.
The leak rate is typically determined as follows. First, the gate valve is closed. The rise rate of pressure is measured using a diaphragm gauge or the like capable of measuring absolute pressure. The leak rate LR is given by LR=R·V [PaL/s], where R [Pa/s] is the measured pressure rise rate and V [L] is the volume of the vacuum chamber. The leak rate is the sum of net (that is, representing the difference between desorption and adsorption) outgas flow rate from the surface of the chamber itself and its internal components, and leak flow rate from the atmosphere. Note that the pressure rise rate R without being multiplied by volume V may be used instead of the leak rate. It is understood, however, that they can be used interchangeably because the volume of the vacuum chamber of the apparatus is always constant.
The plasma etching apparatus further requires the so-called “aging” process when the degree of vacuum has reached a prescribed value. In the aging process, the temperature of the discharging unit is increased by break-in discharge with inert gas, and the inner surface of the process container is conditioned by discharge with actual process gas. If this is not sufficient for stable etching, many dummy wafers may be consecutively processed under the condition of actual product processing before the actual product processing is started. In this way, wet cleaning involves a very large amount of downtime of the apparatus. Reduction of the downtime can increase the amount of time available to the apparatus for actual production, which leads to increased production.
In particular, the time for evacuation usually accounts for a considerable percentage of the time for wet cleaning. It is widely known that evacuation from atmospheric pressure to high or ultrahigh vacuum is attributed to evacuation of water molecules adsorbed on the inner surface of the vacuum chamber and the like (see, for example, J. F. O'Hanlon, User's Guide to Vacuum Technology, John Wiley & Sons, Inc.). Even in the normal evacuation process, although depending on apparatus, it takes several to several tens of hours to reach a prescribed pressure and leak rate. Any leak from the atmosphere may occur due to, for example, small fibers caught in the O-ring or other seal which has prevented the apparatus pressure from decreasing to the prescribed pressure and leak rate. In that case, after a long time is spent in evacuation, the apparatus must be returned to the atmosphere to remove the fibers at the seal, and again evacuated. Such a trouble significantly wastes time.
To solve this problem, in the conventional art, there are a number of efforts for rapidly detecting evacuation abnormality. For example, Fukuzawa et al. has proposed a method of rapidly detecting evacuation abnormality and predicting time to reach the target pressure by comparing measured data of pressure with theoretical pressure change, and a vacuum apparatus having such a prediction control system (see, for example, Japanese Laid-Open Patent Application 2002-346367). It seems that their invention assumes evacuation of a chamber made of stainless steel. However, it is often the case that semiconductor manufacturing apparatus in recent years have a chamber made of aluminum alloy covered with anodized aluminum coating. Furthermore, various materials are used inside the chamber. As a result, it is difficult to determine a theoretical evacuation curve. It therefore seems that their method is difficult to apply to the apparatus having a chamber made of aluminum alloy covered with anodized aluminum coating. Moreover, they do not take into consideration the time for aging the apparatus after evacuation.